The invention concerns a procedure for cooling work pieces by direct heat exchange with a low-boiling liquefied gas.
In industrial practice, work pieces, particularly work pieces of metal, are frequently cooled by means of direct heat exchange with liquid nitrogen. The low coolant temperature of -196.degree. C. guarantees relatively short cooling time in addition to the low end temperature. Examples of this are cold shrinking and pipe frosting. In pipe frosting, the liquid in a pipe is temporarily frozen at one or two locations, i.e., the pipeline is closed, so that repairs can be made on the pipeline.
In the case of small work pieces, the cooling times proper constitute no significant economical factor, since, for instance in cold shrinking, the further processing of the cooled parts limits the production process in time, or, as another example, in pipe frosting, the period when the cold has to be maintained is significantly longer than the duration of the cooling process. However, if the work pieces are larger, the cooling duration increases overproportionally to the volume of the work piece. This is partially unavoidable since the heat conductivity in the interior of the work piece cannot be influenced. An acceleration of the cooling can at most be achieved by means of improved heat transfer between the surface of the work piece and the low-boiling liquefied gas.